1. Technical Field
The present invention relates to a seat belt retractor for a vehicle. More particularly, the present invention relates to a seat belt retractor having a manual cinch mechanism for blocking seat belt withdrawal on demand by a vehicle occupant.
2. Description of the Prior Art
A vehicle seat belt retractor holds a vehicle occupant in a seat by blocking withdrawal of seat belt webbing from the retractor when the seat belt is buckled around the occupant. Some seat belt retractors are constructed to allow an occupant to buckle the seat belt and still be able to move around in the seat. These retractors include an emergency locking mechanism for blocking withdrawal of the seat belt in an emergency.
Notwithstanding the provision of an emergency locking mechanism in a retractor, some seat belt retractors include a manual "cinch" mechanism, by which a vehicle occupant can manually lock the retractor to block further belt withdrawal. U.S. Pat. No. 4,427,164 shows a seat belt retractor with a manual cinch mechanism actuated by a push button. When the push button is actuated, a locking pawl engages a spool locking ratchet wheel. An overcenter spring attached to the locking pawl holds the pawl in engagement with the spool locking ratchet wheel, blocking rotation of the spool in the belt withdrawal direction.
Retractors incorporating the cinch mechanism shown in U.S. Pat. No. 4,427,164 can unintentionally engage the cinch mechanism when the vehicle passes over rough surfaces. The locking pawl is metal in order to withstand locking loads. It also has enough inertia that under certain road conditions, it can unintentionally pivot against the bias of the overcenter spring into engagement with the spool locking ratchet wheel. The overcenter spring then holds the pawl in engagement with the spool locking ratchet wheel, blocking belt withdrawal and possibly causing occupant discomfort, at a time when the vehicle occupant did not intend to actuate the cinch mechanism. The cinch mechanism can only be disengaged by unbuckling the belt or by opening a vehicle door, both of which actions are unsafe when driving.